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He was rushed into emergency surgery at the hospital after the incident.

Security guard and father-of-four Barry Jennings, 48, was shot in the calf and is in a stable condition after also undergoing surgery.

After several hours of waiting in a police holding cell, he was taken back to the hospital to be treated for a broken jaw.

Friends say the former nurse and father-of-two from Rouse Hill had recently been depressed and was suffering financial difficulties, but did not appear to be on drugs.

Police said De Guzman had been arrested for break and enter offences at a friend's home in Colyton before the hospital incident and had been granted bail.

A critical investigation team from North West Metropolitan Region are now looking into the incident.

NSW Police Deputy Commissioner Catherine Burn said Snr Const Warburton had only just begun his shift.

The incident is believed to have happened inside the hospital's emergency department. (9NEWS)Senior Constable Luke Warburton appeared on the TODAY Show in 2012 speaking about the search for Australia's then most-wanted fugitive Malcolm Naden.

“This officer had only just started working, had only just started the shift for the night, had just taken the first call and this is what has occurred,” she said.

Snr Const Warburton, the handler of police dog Chuck, was instrumental in the capture of one of Australia's most wanted fugitives, Malcolm Naden.

In 2012, Chuck brought Naden to heel, biting the murderer on the arm as he emerged from his Hunter Valley hideaway in the dead of night

The shooting highlights the critical need to beef up powers for security guards, the Health Services Union says.

HSU secretary Gerard Hayes said the shooting of a policeman and security guard during a scuffle with a man wielding scissors shows the need for stronger protections.

"We've been saying for some time (we need) to have the power to be able to restrain and detain people," he told reporters outside western Sydney's Nepean Hospital.